Presently, computer graphics, 3D modeling of real-world objects in software, and 3D mechanical design are in widespread use. Accordingly, it is desirable to capture an approximate computer software model of an existing physical object. In many cases, it may suffice for the model to be a “point cloud” of surface points sampled from the physical object. In a more sophisticated model, the points are vertices of abutting planar polygonal patches which approximate the surface of the object. In an even more sophisticated model, the patches are curved, each defined by a bivariate polynomial or rational mathematical function, as in the NURBS surfaces commonly used in computer graphics. Special cases of 3D data entry also rely on parametric entry, where the geometric shape (circle, sphere, cube, etc.) of the object is known and the parametric features are specified in order to be retained during scanning.
Numerous approaches exist which automate or partially automate the process of sampling representative points from the surface of an object. One approach generates a single point at a time, as a contact probe tip is moved across the surface of the object. Traditional coordinate measuring machines (CMMs) as well as handheld magnetic, mechanical, and optical probe tracking systems have historically used this contact probe approach. Computer-aided design (CAD) software can be used to accumulate the measured points and to build therefrom a 3-dimensional model of the surface of the object. An example of a handheld, optically tracked probe and its tracking system are the FlashPoint and 3D Creator products sold by Boulder Innovation Group, Inc. (Boulder, Colo.).
Another approach might include various laser or optical beam non-contact probes, which operate similar to the contact probe approach. However, the “probe tip” is a narrow light beam together with an optical sensor, which accurately measures the length of the ray-like beam to where it intersects the object at a point. That distance together with knowledge of the exact position of the light beam allows computation of the 3-dimensional XYZ coordinates of the point where the beam intersects the surface of the object. By gathering sufficiently dense points from the object, software can create a suitable model of the surface of the object. To date, such non-contact probes are tethered at least by an electronic cable, if not by additional mechanical linkage.
Rather than a single ray-like laser beam, more advanced non-contact scanners project a planar “fan” of light to illuminate many points on the object, where the intersection of the light and the object forms an illuminated stripe or contour line on the object. These scanners are sometimes called “laser stripe triangulation” scanners. One or more video cameras acquire a 2D dimensional image of the contour line from a position offset from the plane of light. In effect, the image of the contour line on each camera simultaneously captures the locations of many surface points all on one plane through the object. This speeds the process of gathering many sample points, while the plane of light (and usually also the receiving camera) is laterally moved so to “paint” some or all of the exterior surface of the object with the plane of light. By knowing the instantaneous position of the camera and the instantaneous position of the plane of light within a object-relative coordinate system when the image was acquired, a computer and software can use triangulation methods to compute the coordinates of illuminated surface points. As the plane is moved to intersect eventually with some or all of the surface of the object, the coordinates of more points are accumulated.
A number of commercially available systems employ the technique of projecting a manually moveable plane of light and imaging the illuminated intersection of the light on the object. Examples include, the U.S. Pat. No. 4,737,032 (Cyberware, Inc., Monterey, Calif.), the FastSCAN (Polhemus Inc., Colchester, Vt.), and K-Scan (Metris N. V., Leuven, Belgium).
Other systems project more than one plane of light onto the object, or project even more complex patterns of structured light. Examples are Metris's X-Scan product and U.S. Pat. No. 7,009,717 by Coppenolle et al, which is incorporated herein by reference.
Other systems project a pattern of light that is modulated by sequentially increasing and decreasing the light line widths, sometimes using a Gray Code Sequence. One variation of this moves the line pattern over the object, referred to as “phase shift encoding”. Examples of these systems are GFM Messtechnik, ABW-3D, both of Germany, Opton (Japan), stereoSCAN by Breackmann and GOM of Germany.
To date, such non-contact scanners are tethered at least by an electronic cable, if not by further mechanical linkage. For example, see U.S. Pat. No. 6,611,617 of Crampton.